1. Field of the Invention
The present invention relates to object detection portals and more specifically to a system in which locations of detected objects are displayed as an indicator overlay on a video image of the volume being scanned.
2. Discussion of Related Art
A very common form of object detection portal is a metal detector archway such as a weapons detector portal used for security screening. Metal detection portals typically operate on the principles of inductive and/or magnetic detection of conductive or ferromagnetic objects such as guns or knives. Typically a person to be inspected walks through an archway structure containing an array of inductive coils and any resultant perturbation of the inductive coil fields is determined. Normally this perturbation is quantified by portal electronics to produce a signal whose magnitude is compared to a preset threshold value. If the signal is equal to or greater than the threshold value the portal will make an indication to the operator that the individual inspected may be carrying a weapon. The presence of a potential threat is often indicated by an audio tone or may be indicated by another signal.
Such systems are notoriously imprecise in distinguishing between benign objects and dangerous objects. False alarm rates typically range from 10% to 40%. The result of a false indication is that screening personnel need to conduct a secondary screening. A subject is required to divest further objects and be rescanned. The secondary screening may consist of further scans in the portal, scans with a hand-held metal detector, a manual “pat-down” or a combination of these methods. The time for the usual divesting prior to a scan and a single scan is typically 15 seconds. With false alarms, screening time for an individual can increase up to two minutes. The typical portal does not contain any means for restraining an individual who does not successfully complete the screening process.
One system which provides further information about the location of detected objects is disclosed in U.S. Pat. No. 6,150,810. In this prior art system, after determining the approximate horizontal and vertical locations of detected objects, as well as making some determination of the signal from each object, resulting data may be presented on a display. The display may include a computer-generated picture of a passageway and may also include a computer-generated silhouette or image of a person in the passageway. The display further includes indicator highlights of detected ferromagnetic objects. Alternatively, the display may include the highlights on a video “snap-shot” of the passageway. When secondary screening is conducted, a new scan must be performed. Object location data is not carried over from a first screening to a second screening. An operator having identified an object in a primary scan could mistakenly target a different area for a secondary scan.
It is highly desirable to provide a system in which further information is provided to a screener to improve the use and effectiveness of screening data indicating object location. It is also desirable to improve security by incorporating a condition-responsive restraint in a screening portal.